To achieve a reliable result on a visual field test it is important to correct the patient's refractive error, since refractive blur will reduce the visual sensitivity to perimetric stimuli. Today, it is standard practice to reduce the refractive error to within 1 diopter, which would produce less than one decibel of depression of the hill of vision when testing with a Goldmann size II stimulus (see for example Anderson D. R et al Automated Static Perimetry Second Edition 1999: Mosby Inc.) The use of a set of standard ophthalmic trial lenses is the commonly used method of correcting a patient's refractive error. The perimetry operator selects and inserts lenses into the line of vision of the patient based on a previously determined refractive value for the patient. A large fraction of all patients require such correction due to myopia, hyperopia or presbyopia. Although a set of trial lenses are available in most clinical settings, they provide a cumbersome and time consuming method of reducing refractive blur during a visual field test.
There are also a number of negatives associated with trial lenses leading to reduced reliability of the visual field test. Trial lens “rim artifact”, where the trial lens frame blocks parts of the visual filed, can be confused by inexperienced clinicians as actual field loss. Mistakes in selecting the correct trial lens can cause a general depression of the visual field. Furthermore, the patient's comfort is often reduced by the use of trial lenses and overall workflow in the office setting is significantly slowed down.
It is therefore a general objective of this invention to provide both a method and an apparatus to improve the reliability of the visual field test, improve patient comfort, and reduce errors and possible mistakes associated with the use of trial lenses. Furthermore, the invention will improve workflow and the throughput of the clinics.